Transmitting and Receiving Signals

ABSTRACT

In one example aspect, a method of transmitting signals is provided, the method comprising transmitting signals using one or more first subcarriers only from a first antenna, wherein the signals transmitted from the first antenna comprise first signals based on data, and transmitting signals using one or more second subcarriers different from the one or more first subcarriers only from a second antenna, wherein the signals transmitted from the second antenna comprise second signals based on the data.

TECHNICAL FIELD

Examples of the present disclosure relate to transmitting and receivingsignals, for example in multi-antenna systems.

Background

Some applications of wireless communications may require low latencyand/or high reliability. For example, some applications ofultra-reliable low latency communications (URLLC) may require one ormore of small packet sizes, low latency and high reliability (e.g. lowpacket error rate, PER). Diversity techniques can be helpful inachieving high reliability.

In multi-antenna wireless systems (e.g. multiple-input multiple-output,MIMO), spatial degrees of freedom can be employed to increase either themultiplexing gain or the diversity gain, but there is a fundamentaltradeoff between the two gains, and it may not be possible to optimizethem both simultaneously.

SUMMARY

One aspect of the present disclosure provides a method of transmittingsignals. The method comprises transmitting signals using one or morefirst subcarriers only from a first antenna, wherein the signalstransmitted from the first antenna comprise first signals based on data.The method also comprises transmitting signals using one or more secondsubcarriers different from the one or more first subcarriers only from asecond antenna, wherein the signals transmitted from the second antennacomprise second signals based on the data.

Another aspect of the present disclosure provides a method of receivingsignals. The method comprises receiving, at a first reception antenna,signals transmitted using one or more first subcarriers only from afirst transmission antenna, wherein the signals transmitted from thefirst transmission antenna comprise first signals based on data. Themethod also comprises receiving, at the first reception antenna, signalstransmitted using one or more second subcarriers different from the oneor more first subcarriers only from a second transmission antenna,wherein the signals transmitted from the second transmission antennacomprise second signals based on the data.

A further aspect of the present disclosure provides apparatus fortransmitting signals. The apparatus comprises a processor and a memory.The memory contains instructions executable by the processor such thatthe apparatus is operable to transmit signals using one or more firstsubcarriers only from a first antenna, wherein the signals transmittedfrom the first antenna comprise first signals based on data, andtransmit signals using one or more second subcarriers different from theone or more first subcarriers only from a second antenna, wherein thesignals transmitted from the second antenna comprise second signalsbased on the data.

A still further aspect of the present disclosure provides apparatus forreceiving signals. The apparatus comprises a processor and a memory. Thememory contains instructions executable by the processor such that theapparatus is operable to receive, at a first reception antenna, signalstransmitted using one or more first subcarriers only from a firsttransmission antenna, wherein the signals transmitted from the firsttransmission antenna comprise first signals based on data, and receive,at the first reception antenna, signals transmitted using one or moresecond subcarriers different from the one or more first subcarriers onlyfrom a second transmission antenna, wherein the signals transmitted fromthe second transmission antenna comprise second signals based on thedata.

An additional aspect of the present disclosure provides apparatus fortransmitting signals.

The apparatus is configured to transmit signals using one or more firstsubcarriers only from a first antenna, wherein the signals transmittedfrom the first antenna comprise first signals based on data, andtransmit signals using one or more second subcarriers different from theone or more first subcarriers only from a second antenna, wherein thesignals transmitted from the second antenna comprise second signalsbased on the data.

Another aspect of the present disclosure provides apparatus forreceiving signals. The apparatus is configured to receive, at a firstreception antenna, signals transmitted using one or more firstsubcarriers only from a first transmission antenna, wherein the signalstransmitted from the first transmission antenna comprise first signalsbased on data, and receive, at the first reception antenna, signalstransmitted using one or more second subcarriers different from the oneor more first subcarriers only from a second transmission antenna,wherein the signals transmitted from the second transmission antennacomprise second signals based on the data.

A further aspect of the present disclosure provides apparatus fortransmitting signals. The apparatus comprises a first transmittingmodule configured to transmit signals using one or more firstsubcarriers only from a first antenna, wherein the signals transmittedfrom the first antenna comprise first signals based on data. Theapparatus also comprises a second transmitting module configured totransmit signals using one or more second subcarriers different from theone or more first subcarriers only from a second antenna, wherein thesignals transmitted from the second antenna comprise second signalsbased on the data.

A still further aspect of the present disclosure provides apparatus forreceiving signals. The apparatus comprises a first receiving moduleconfigured to receive, at a first reception antenna, signals transmittedusing one or more first subcarriers only from a first transmissionantenna, wherein the signals transmitted from the first transmissionantenna comprise first signals based on data. The apparatus alsocomprises a second receiving module configured to receive, at the firstreception antenna, signals transmitted using one or more secondsubcarriers different from the one or more first subcarriers only from asecond transmission antenna, wherein the signals transmitted from thesecond transmission antenna comprise second signals based on the data.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of examples of the present disclosure, and toshow more clearly how the examples may be carried into effect, referencewill now be made, by way of example only, to the following drawings inwhich:

FIG. 1 is a flow chart of an example of a method of transmittingsignals;

FIG. 2 shows an example of signals transmitted simultaneously from atransmission system;

FIG. 3 shows an example of a method of receiving signals;

FIG. 4 shows an example of a transmitter;

FIG. 5 shows an example of a transmitter;

FIG. 6 shows an example of apparatus for transmitting signals;

FIG. 7 shows an example of apparatus for receiving signals;

FIG. 8 shows an example of apparatus for transmitting signals; and

FIG. 9 shows an example of apparatus for receiving signals.

DETAILED DESCRIPTION

The following sets forth specific details, such as particularembodiments or examples for purposes of explanation and not limitation.It will be appreciated by one skilled in the art that other examples maybe employed apart from these specific details. In some instances,detailed descriptions of well-known methods, nodes, interfaces,circuits, and devices are omitted so as not obscure the description withunnecessary detail. Those skilled in the art will appreciate that thefunctions described may be implemented in one or more nodes usinghardware circuitry (e.g., analog and/or discrete logic gatesinterconnected to perform a specialized function, ASICs, PLAs, etc.)and/or using software programs and data in conjunction with one or moredigital microprocessors or general purpose computers. Nodes thatcommunicate using the air interface also have suitable radiocommunications circuitry. Moreover, where appropriate the technology canadditionally be considered to be embodied entirely within any form ofcomputer-readable memory, such as solid-state memory, magnetic disk, oroptical disk containing an appropriate set of computer instructions thatwould cause a processor to carry out the techniques described herein.

Hardware implementation may include or encompass, without limitation,digital signal processor (DSP) hardware, a reduced instruction setprocessor, hardware (e.g., digital or analogue) circuitry including butnot limited to application specific integrated circuit(s) (ASIC) and/orfield programmable gate array(s) (FPGA(s)), and (where appropriate)state machines capable of performing such functions.

Examples of the present disclosure provide a communication systemwhereby data is sent using multiple carriers from multiple antennas.However, a particular subcarrier is only sent from one antenna.Therefore, in some examples, signals transmitted from different antennascan be considered as orthogonal, where orthogonal subcarriers are used.In some cases, the communication system may be considered as multiplesingle-input single-output (SISO) or single-input multiple-output (SIMO)systems, which may reduce overhead and/or processing complexity comparedto a MIMO system. Furthermore, in some examples, as not all subcarriersare transmitted from a single antenna, signals transmitted from a singleantenna can be increased in power without increasing the overall powertransmitted using all available subcarriers from a single antenna.

RECTIFIED SHEET (RULE 91) ISA/EP

FIG. 1 is a flow chart of an example of a method 100 of transmittingsignals. The method 100 comprises, in step 102, transmitting signalsusing one or more first subcarriers only from a first antenna, whereinthe signals transmitted from the first antenna comprise first signalsbased on data. Step 104 of the method comprises transmitting signalsusing one or more second subcarriers different from the one or morefirst subcarriers only from a second antenna, wherein the signalstransmitted from the second antenna comprise second signals based on thedata. The signals transmitted from the second antenna may for example betransmitted simultaneously with the signals transmitted from the firstantenna.

Therefore, for example, where a transmitter or a transmission systemincludes multiple antennas, a signal is transmitted only from one ofthose antennas, and not from any of the other antennas (e.g. the method100 comprises refraining from transmitting signals using the one or moresecond subcarriers from the first antenna, and/or refraining fromtransmitting signals using the one or more first subcarriers from thesecond antenna). Signals transmitted from a particular antenna may insome examples comprise multiple subcarriers that are not transmittedfrom any of the other antennas.

The signals from each antenna are based on the data. That is, forexample, the same data may be used to form signals transmitted from eachantenna. However, different modulation schemes, coding schemes,interleaving schemes, scrambling schemes, encryption schemes and/or anyother data manipulation schemes may be used for different antennas insome examples, though in other examples one or more of the same schemesmay be used across the antennas.

FIG. 2 shows an example of signals transmitted simultaneously from atransmission system that includes four antennas. Signals 202 aretransmitted from a first antenna TX1. Signals 204 are transmitted from asecond antenna TX2. Signals 206 are transmitted from a third antennaTX3. Signals 208 are transmitted from a fourth antenna TX4. Each blockrepresents a particular subcarrier, with blocks representing the samesubcarrier arranged vertically. A shaded block indicates that no signalis transmitted from that subcarrier from that antenna. The signalstransmitted from each antenna are based on data comprising groups of oneor more bits d0, d1, d2 and d3. In FIG. 2, a block containing one ofthese indicates that a signal based on that group of one or more bits istransmitted from that subcarrier from that antenna.

For example, a signal based on bits d0 is transmitted from a firstsubcarrier only from antenna TX1. A signal on the next subcarrier,adjacent to the first subcarrier, is transmitted only from TX2 based onbits d1. A signal on the next subcarrier is transmitted only from TX3based on bits d2. A signal on the next subcarrier is transmitted onlyfrom TX4 based on bits d3. A signal on the next subcarrier istransmitted only from TX1 based on bits d1, and so on.

In the example shown, transmitting signals based on the same data fromdifferent antennas may provide spatial diversity, whereas transmittingsignals based on the same group of bits from different subcarriers(which are transmitted on different antennas) may provide frequencyand/or spatial diversity. In the example shown, signals on adjacentsubcarriers are not based on the same group of one or more bits, whichmay provide further frequency diversity. In the example shown, from eachantenna, signals based on the data are transmitted on four out ofsixteen available subcarriers, while no signal is transmitted on theremaining twelve subcarriers from that antenna. Therefore, compared to atransmission system where signals are transmitted on all subcarriersfrom an antenna, the signals transmitted from each antenna can beincreased in power by a factor of four without increasing the overalltransmission power.

In other examples, there may be any number of two or more transmitantennas, there may be any number of subcarriers, and the signals fromeach antenna may be on any subcarrier and based on any bits of the data.The subcarriers may in some examples be orthogonal.

In some examples, the data comprises one or more data portions (e.g. oneor more groups of one or more bits), and transmitting the signals fromthe first and second antennas comprises, for each data portion,transmitting at least one first symbol using a respective one of the oneor more first subcarriers from the first antenna, and transmitting atleast one second symbol using a respective one of the one or more secondsubcarriers from the second antenna. Therefore, for example, each dataportion can be mapped to a respective subcarrier from each transmitantenna. In some examples, for each data portion, the respective one ofthe one or more first subcarriers and the respective one of the one ormore second subcarriers are non-adjacent. This may provide frequencydiversity, as interference affecting adjacent subcarriers may not affectsignals based on the same data portion. In some examples, the at leastone first symbol and the at least one second symbol are identical,whereas in other examples they may be different (e.g. where there is adifferent mapping of data portions to symbols between differentantennas)

In some examples, the method 100 comprises transmitting signals from oneor more further antennas, wherein, for each further antenna,transmitting signals from the further antenna comprises transmittingsignals using respective one or more further subcarriers only from thefurther antenna, wherein the signals transmitted from the furtherantenna comprise second signals based on the data, and wherein therespective one or more further subcarriers are different from the one ormore first subcarriers and the one or more second subcarriers. Thus,there may be two, three, four or more transmit antennas, eachtransmitting signals using subcarriers unique to that antenna.

In some examples, the method 100 comprises encoding the data and mappingportions of the encoded data to first symbols according to a firstmodulation scheme. The method 100 also comprises performing an inversediscrete Fourier transform on the first symbols to form the firstsignals, mapping portions of the encoded data to second symbolsaccording to a second modulation scheme, and performing an inversediscrete Fourier transform on the second symbols to form the secondsignals. In such examples, the same encoding scheme may be used totransmit signals from each of the antennas based on the data, whereasthe modulation schemes may be different between antennas or may be thesame. In some examples, the method comprises interleaving the data orthe symbols. This may provide frequency and/or time diversity.

In some examples, the method comprises forming the first signals byencoding portions of the data according to a first encoding scheme toform first encoded data, mapping the first encoded data to first symbolsaccording to a first modulation scheme, and performing an inversediscrete Fourier transform and multiplication by a complex waveform onthe first symbols to form the first signals. The method 100 alsocomprises forming the second signals by encoding portions of the dataaccording to a second encoding scheme to form second encoded data,mapping the second encoded data to second symbols according to a secondmodulation scheme, and performing an inverse discrete Fourier transformand multiplication by a complex waveform on the second symbols to formthe first signals. Thus, signals transmitted from different antennas canbe formed using a respective modulation and encoding scheme, that may bethe same as or different from a modulation and encoding scheme used toform signals transmitted from other antennas.

In some examples, the first modulation scheme is different from thesecond modulation scheme, though in other examples the modulationschemes may be the same.

In some examples, the data comprises a training field (e.g. longtraining field, LTF) and a data field. The training field may forexample be used by a receiver to measure characteristics of the channelbetween a particular transmit antenna and a receiver. In some examples,because each subcarrier is only transmitted from a single antenna, onlyone training field may be transmitted in each cycle. Other transmissionschemes such as MIMO or MISO that transmit using the same subcarriersimultaneously from multiple antennas may for example require moretraining fields to be transmitted (e.g. one per transmit antenna,non-simultaneously), or may spread the LTF using orthogonal cover codes.

FIG. 3 shows an example of a method 300 of receiving signals. Forexample, the signals may be transmitted according to the method 100described above with reference to FIGS. 1 and 2. The method 300comprises, in step 302, receiving, at a first reception antenna, signalstransmitted using one or more first subcarriers only from a firsttransmission antenna, wherein the signals transmitted from the firsttransmission antenna comprise first signals based on data. The method300 also comprises, in step 304, receiving, at the first receptionantenna, signals transmitted using one or more second subcarriersdifferent from the one or more first subcarriers only from a secondtransmission antenna, wherein the signals transmitted from the secondtransmission antenna comprise second signals based on the data.

Therefore, for example, signals received at the first antenna on aparticular subcarrier are received from only one of the transmitantennas. The method 300 may therefore comprise for example receiving nosignals transmitted from the first transmission antenna on the one ormore second subcarriers, and/or receiving no signals transmitted fromthe second transmission antenna on the one or more first subcarriers.

In some examples, the signals received at the first reception antennacan be considered as a plurality of single-input single-output (SISO)signals and processed accordingly (e.g.

channel estimation and/or equalization). In some examples, where thereare multiple reception antennas, the signals received at the multiplereception antennas can be considered as a plurality of single-inputmultiple-output (SIMO) signals and processed accordingly.

The received signals may be transmitted from any number of two or moreantennas. Therefore, in some examples, the method 300 comprisesreceiving signals transmitted from one or more further transmissionantennas, wherein, for each further transmission antenna, receivingsignals transmitted from the further transmission antenna comprisesreceiving signals transmitted using respective one or more furthersubcarriers only from the further transmission antenna. The signalstransmitted from the further transmission antenna comprise secondsignals based on the data, and wherein the respective one or morefurther subcarriers are different from the one or more first subcarriersand the one or more second subcarriers.

The signals received on each subcarrier may be demodulated and/ordecoded accordingly. The demodulation and/or decoding scheme may differbetween subcarriers (e.g. if the subcarriers were transmitted fromdifferent antennas) or may be the same between subcarriers.

Particular examples and embodiments will now be described below.

Examples of the present disclosure may provide Spatial Multiple CarrierModulation (SMCM), transmitting a subcarrier only from a particularantenna, that may provide diversity gains when both the transmitter andreceiver possess multiple antennas. Traditionally, good link budget andmultiple antennas may be used to increase the communication speed. Incontrast, SMCM utilizes a good link budget and multiple antennas toincrease diversity (which can in turn be used to provide highreliability). It differs from for example multiple-input multiple-outputdual-carrier modulation (MIMO-DCM) in several respects.

Firstly, SMCM may require less overhead, because only one long trainingfield (LTF) may be used regardless of the number of spatial streams.With URLLC, which may have short packets consisting of as little as oneOFDM data symbol, this difference can have a substantial impact in theoverall number of users that can be supported.

Secondly, the receiver algorithms may have lower complexity than thecorresponding algorithms for MIMO-DCM. This can be an advantageparticularly in low end devices with limited processing capabilities.

Thirdly, in MIMO-DCM the data is duplicated, while the constellationorder is also increased. However, the power in each subcarrier is keptconstant. In embodiments described herein, the data may be duplicatedand the constellation order may also be increased, but a duplication ofthe data may be accompanied by a halving of the number of non-zerosub-carriers, which in turn may allow a 3 dB boost of the power of eachnon-zero subcarrier without an increase in the total transmit power.

FIG. 4 shows an example of a SMCM transmitter 400 that includes Ntransmit antennas.

Data bits are provided to encoder/interleaver block 402 that encodes andinterleaves the data bits. The encoded and interleaved data is providedto orthogonal constellation mappers 404, 406, 408, each mapperassociated with a respective one of the transmit antennas. The mappers404, 406, 408 may allocate orthogonal sub-carriers to the respectivespatial streams to be transmitted from each antenna. That is, forexample, the set of used sub-carriers in any given spatial stream areorthogonal to the set of used sub-carriers used in any other stream. Thefrequency domain symbols may also be shifted or interleaved in order toexploit frequency diversity. The output of each mapper 404, 406, 408 isprovided to a respective inverse discrete Fourier transform (IDFT) block410, 412, 414, and the output of each IDFT block is provided to arespective transmit antenna.

FIG. 5 shows an example of another SMCM transmitter 500 that includes Ntransmit antennas. Data is provided to a duplicator 502 that duplicatesthe data and provides the data to respective modulation and coding (MCSencode) blocks 504, 506, 508, each associated with a respective transmitantenna. The outputs of the MCS encode blocks 504, 506, 508 may each beinterleaved by interleaver 510. Outputs of the interleaver are providedto respective IDFT blocks 512, 514, 516, each associated with arespective transmit antenna. The output of each IDFT block 512, 514, 516is provided to a respective multiplier 518, 520, 522 and multiplied by acomplex waveform, in this example e^(jtw) ^(x) ,x=1, . . . , N. Theoutputs of the multipliers 518, 520, 522 are provided to respectivetransmit antennas.

There are two particular differences of the transmitter 500 of FIG. 5compared to the transmitter 400 of FIG. 4. The first difference is thatthe encoding is now performed on each copy of the data from theduplicator 502 individually, allowing a scheme where different codingrates (and/or modulation orders) can be used on different subcarriers.The second difference is that the IDFT may not be performed over thefull band, but just for the active part of the band. For example, ifthere are 64 subcarriers and four antenna ports, four IDFTs of size 16can be used. The resulting signals are then converted to the appropriatepart of the band by a multiplication with a complex waveform atmultipliers 518, 520, 522.

As an example, an OFDM system may have sixteen active/availablesubcarriers and 32 code bits per OFDM symbol. The payload can be mappedto sixteen QPSK constellation symbols, which modulate the phase of eachof the active subcarriers. Spatial expansion can be used to map the OFDMsymbols to four transmitters. According to examples of the presentdisclosure, diversity can be increased by mapping the payload to four256-QAM symbols, such as for example denoted d0 to d3 in FIG. 2, if thegroups of bits d0, d1, d2 and d3 are 256-QAM symbols for example. Sincethere are four used and twelve muted subcarriers in each transmitterchain, the power of the frequency domain symbols can be boosted by afactor of four (6 dB) from each antenna, while keeping the totaltransmitted power equal to that of the OFDM system. In addition, sincethe symbols d0 to d3 are repeated four times, coherent combining at thereceiver may result in a 6 dB processing gain. In summary, the combinedeffect of the power boost and the processing gain may result in anincrease of SNR at the receiver, but may not result in packet error rate(PER) reduction when compared to a prior art system, since theconstellation order is also increased. This is due to the fact thathigher order constellations operate at higher SNR than lower orderconstellations. In this example, the power boost gives a 6 dB SNR gain,while the repetition yields another 6 dB in processing gain, resultingin a total SNR gain of 12 dB. However, in many wireless systems, 256-QAMtypically has an operating SNR that is around 18 dB higher than theoperating SNR of QPSK, so that there may not be noticeable differencesin PER due to the SNR. Rather, the main advantages of examples of thepresent disclosure may include gains in diversity and/or low overhead,and/or low TX/RX complexity when compared to prior art systems. In thisexample, a SISO system using spatial expansion may exhibit lessdiversity than examples of the present disclosure, because it may notexploit all the spatial degrees of freedom available. Examples of thisdisclosure, with a larger diversity gain, may result a smaller outageprobability, which is a desirable property in for example URLLC. On theother hand, a MIMO system could exploit all the spatial degrees offreedom available, but would require considerably more training or pilotoverhead. In addition, such a MIMO system may require more advancedreceivers.

While the overhead can be negligible in some wireless broadbandapplications, it can be significant in URLLC or Industrial loTapplications when data payloads are small. In such circumstances,embodiments of this disclosure may result in lower latency and/or highersystem capacity.

SIMO receiver algorithms (SIMO channel estimation, SIMO equalization)may also be employed at a receiver. This is a consequence of the spatialstreams being orthogonal in the frequency domain. As an illustrativeexample, a transmitter may transmit signals from four antennas, similarto as shown in FIG. 2, and a receiver may have two receive antennas. Thereceived signals, corresponding to subcarrier number n, are y₁(n) andy₂(n). The channel between transmit antenna m and receive antenna k ish_(km)(n), and w_(k)(n) are noise samples. Suppose that it is desired toestimate the transmitted symbol d0 (where d0, d1, d2 and d3 representtransmitted symbols). d0 is transmitted in subcarriers numbers 1, 8, 11and 14. Hence, the following model describes the received signalscontaining the symbol d0.

${\begin{bmatrix}{y_{1}(1)} \\{y_{2}(1)}\end{bmatrix} = {{\begin{bmatrix}{h_{11}(1)} \\{h_{21}(1)}\end{bmatrix}d\; 0} + \begin{bmatrix}{w_{1}(1)} \\{w_{2}(1)}\end{bmatrix}}},{\begin{bmatrix}{y_{1}(8)} \\{y_{2}(8)}\end{bmatrix} = {{\begin{bmatrix}{h_{14}(8)} \\{h_{24}(8)}\end{bmatrix}d\; 0} + \begin{bmatrix}{w_{1}(8)} \\{w_{2}(8)}\end{bmatrix}}},{\begin{bmatrix}{y_{1}\left( {11} \right)} \\{y_{2}\left( {11} \right)}\end{bmatrix} = {{\begin{bmatrix}{h_{13}\left( {11} \right)} \\{h_{23}\left( {11} \right)}\end{bmatrix}d\; 0} + \begin{bmatrix}{w_{1}\left( {11} \right)} \\{w_{2}\left( {11} \right)}\end{bmatrix}}},{\begin{bmatrix}{y_{1}\left( {14} \right)} \\{y_{2}\left( {14} \right)}\end{bmatrix} = {{\begin{bmatrix}{h_{12}\left( {14} \right)} \\{h_{22}\left( {14} \right)}\end{bmatrix}d\; 0} + {\begin{bmatrix}{w_{1}\left( {14} \right)} \\{w_{2}\left( {14} \right)}\end{bmatrix}.}}}$

This is equivalent to 4 parallel 1×2 SIMO systems. Defining

Y=[y ₁(1), y ₂(1), y ₁(8), y ₂(8), y ₁(11), y ₂(11), y ₁(14), y ₂(14)]^(T)

and

H=[h ₁₁(1), h ₁₁(1), h ₁₄(8), h ₂₄(8), h ₁₃(11), h ₂₃(11), h ₁₂(14), h₂₂(14)]^(T),

The model can be rewritten in the form

Y=H·d0+W,

Where W is a noise vector. An estimate

of d0 can be obtained using e.g. maximum ratio combining (MRC)processing:

$= {\frac{H^{*}}{{H}^{2}}{Y.}}$

As illustrated in the example shown in FIG. 4, SMCM generates a numberof duplicates of the encoded data bits. In examples of SMCM thediversity gain can be tuned by changing one or more of the modulationorder, frequency domain interleaving, the code rate and the antenna portmapping.

An example SIMO system may consist of four transmit antennas and receiveantennas, employing single layer transmission with spatial expansion.Suppose that a data packet consists of only two OFDM symbols, the firsta long training field (LTF) for channel estimation and the second a datasymbol. Further, suppose that the payload consists of 120 informationbits and that the code rate is ½. With for example 240 active/availablesubcarriers, the code bits can be mapped to one OFDM data symbol usingBPSK frequency domain symbols labeled s(0), . . . , s(239). Since thereis only one spatial stream, it can be mapped to the four transmitantenna ports, for example by means of spatial expansion.

According to examples of the present disclosure, the same packet formatcan be used, comprising one LTF followed by one data symbol. The LTF canbe identical to the LTF used in the above described SISO system in someexamples, consisting of 240 frequency domain symbols t(0), . . . ,t(239). The constellation, frequency domain and spatial mappings can beas follows in some examples.

-   -   1. Antenna ports Tx1 and Tx2:        -   a. For the LTF, the even numbered frequency domain symbols            t(0), t(2), . . . , t(236), t(238) are mapped to subcarriers            1,3,5, . . . , 239 (e.g. use only every other subcarrier),            and all other subcarriers are muted. Boost the power of            frequency domain symbols by a factor of two (e.g. compared            to a system that uses all carriers simultaneously). This            layer is mapped to the two transmit antenna ports Tx1 and            Tx2 by means of spatial expansion.        -   b. For the data symbol, use subcarriers 1,3,5, . . . , 239            (e.g. use only every other subcarrier), and mute all other            subcarriers. The code bits are mapped to 120 QPSK            constellation symbols labeled d(0), . . . , d(119). Further,            this layer is mapped to the two transmit antenna ports Tx1            and Tx2 by means of spatial expansion. Moreover, the power            of the frequency domain symbols is boosted by a factor 2.    -   2. Antenna ports Tx3 and Tx4:        -   a. For the LTF, the odd numbered frequency domain symbols            t(1), t(3), . . . , t(237), t(239) are mapped to subcarriers            2,4,6, . . . , 240 (e.g. use only every other subcarrier),            and all other subcarriers are muted. Boost the power of            frequency domain symbols by a factor two. This layer is            mapped to the two transmit antenna ports Tx3 and Tx4 by            means of spatial expansion.        -   b. For the data symbol, use subcarriers 2,4,6, . . . , 238,            240 (e.g. use only every other subcarrier), and mute all            other subcarriers. The code bits are mapped to 120 QPSK            constellation symbols labeled d(60),d(61), . . . , d(119),            d(0), . . . , d(59), the same symbols transmitted through            antenna ports Tx1 and Tx2 but cyclically shifted 60 steps.            Further, this layer is mapped to the two transmit antenna            ports Tx3 and Tx4 by means of spatial expansion. Moreover,            the power of the frequency domain symbols is boosted by a            factor two.

The power boost by a factor 2 does not increase the total transmittedpower when compared to the SISO system, since every second subcarrier ismuted in each layer.

According to further examples of the present disclosure, the same packetformat can be used, comprising one LTF followed by one data symbol. TheLTF can be identical to the

LTF used in the SISO system in some examples. The constellation,frequency domain and spatial mappings can be as follows in someexamples.

-   -   1. Antenna port Tx1:        -   a. For the LTF, the frequency domain symbols t(0), t(4), . .            . , t(232), t(236) are mapped to subcarriers 1,5, . . . ,            237 (e.g. use only every fourth subcarrier), and all other            subcarriers are muted. Boost the power of frequency domain            symbols by a factor of four. This layer is mapped to the            transmit antenna port Tx1.        -   b. For the data symbol, use subcarriers 1,5, . . . , 237            (e.g. use only every fourth subcarrier), and mute all other            subcarriers. The code bits are mapped to 60 16-QAM            constellation symbols labeled d(0), . . . , d(59). Further,            this layer is mapped to transmit antenna port Tx1. Moreover,            the power of the frequency domain symbols is boosted by a            factor four.    -   2. Antenna port Tx2:        -   a. For the LTF, the frequency domain symbols t(1), t(5), . .            . , t(233), t(237) are mapped to subcarriers 2,6, . . . ,            238 (e.g. use only every fourth subcarrier), and all other            subcarriers are muted. Boost the power of frequency domain            symbols by a factor of four. This layer is mapped to the            transmit antenna port Tx2.        -   b. For the data symbol, use subcarriers 2,6, . . . , 238            (e.g. use only every fourth subcarrier), mute all other            subcarriers. The code bits are mapped to 60 16-QAM            constellation symbols labeled d(45), . . . , d(59), d(0), .            . . . , d(44), the same symbols transmitted through transmit            antenna port Tx1 but cyclically shifted 15 steps. Further,            this layer is mapped to transmit antenna port Tx2. Moreover,            the power of the frequency domain symbols is boosted by a            factor of four.    -   3. Antenna port Tx3:        -   a. For the LTF, the frequency domain symbols t(2), t(6), . .            . , t(234), t(238) are mapped to subcarriers 3,7, . . . ,            239 (e.g. use only every fourth subcarrier), and all other            subcarriers are muted. Boost the power of frequency domain            symbols by a factor of four. This layer is mapped to the            transmit antenna port Tx2.        -   b. For the data symbol, use subcarriers 3,7, . . . , 239            (e.g. use only every fourth subcarrier), and mute all other            subcarriers. The code bits are mapped to 60 16-QAM            constellation symbols labeled d(30) , . . . , d(59), d(0), .            . . , d(29), the same symbols transmitted through transmit            antenna port Tx1 but cyclically shifted 30 steps. Further,            this layer is mapped to transmit antenna port Tx3. Moreover,            the power of the frequency domain symbols is boosted by a            factor of four.    -   4. Antenna port Tx4:        -   a. For the LTF, the frequency domain symbols t(3), t(7), . .            . , t(235), t(239) are mapped to subcarriers 4,8, . . . ,            240 (use only every fourth subcarrier), and all other            subcarriers are muted. Boost the power of frequency domain            symbols by a factor of four. This layer is mapped to the            transmit antenna port Tx2.        -   b. For the data symbol, use subcarriers 4,8, . . . , 240            (e.g. use only every fourth subcarrier), mute all other            subcarriers. The code bits are mapped to 60 16-QAM            constellation symbols labeled d(15), . . . , d(59), d(0),            d(14), the same symbols transmitted through transmit antenna            port Tx1 but cyclically shifted 45 steps. Further, this            layer is mapped to transmit antenna port Tx4. Moreover, the            power of the frequency domain symbols is boosted by a factor            of four.

The power boost by a factor of four does not increase the totaltransmitted power when compared to the SISO system, since every fourthsubcarrier is muted in each layer.

FIG. 6 shows an example of apparatus 600 for transmitting signals. Theapparatus 600 comprises a processor 602 and a memory 604. The memory 604contains instructions executable by the processor 602 such that theapparatus 600 is operable to transmit signals using one or more firstsubcarriers only from a first antenna, wherein the signals transmittedfrom the first antenna comprise first signals based on data, transmitsignals using one or more second subcarriers different from the one ormore first subcarriers only from a second antenna, wherein the signalstransmitted from the second antenna comprise second signals based on thedata. In some examples, the apparatus 600 may carry out the method 100shown in FIG. 1.

FIG. 7 shows an example of apparatus 700 for receiving signals. Theapparatus 700 comprises a processor 702 and a memory 704. The memory 704contains instructions executable by the processor 702 such that theapparatus 700 is operable to receive, at a first reception antenna,signals transmitted using one or more first subcarriers only from afirst transmission antenna, wherein the signals transmitted from thefirst transmission antenna comprise first signals based on data, andreceive, at the first reception antenna, signals transmitted using oneor more second subcarriers different from the one or more firstsubcarriers only from a second transmission antenna, wherein the signalstransmitted from the second transmission antenna comprise second signalsbased on the data. In some examples, the apparatus 700 may carry out themethod 300 shown in FIG. 3.

FIG. 8 shows an example of apparatus 800 for transmitting signals. Theapparatus 800 comprises a first transmitting module 802 configured totransmit signals using one or more first subcarriers only from a firstantenna, wherein the signals transmitted from the first antenna comprisefirst signals based on data. The apparatus 800 also comprises a secondtransmitting module configured to transmit signals using one or moresecond subcarriers different from the one or more first subcarriers onlyfrom a second antenna, wherein the signals transmitted from the secondantenna comprise second signals based on the data.

FIG. 9 shows an example of apparatus 900 for receiving signals. Theapparatus 900 comprises a first receiving module 902 configured toreceive, at a first reception antenna, signals transmitted using one ormore first subcarriers only from a first transmission antenna, whereinthe signals transmitted from the first transmission antenna comprisefirst signals based on data. The apparatus 900 also comprises a secondreceiving module configured to receive, at the first reception antenna,signals transmitted using one or more second subcarriers different fromthe one or more first subcarriers only from a second transmissionantenna, wherein the signals transmitted from the second transmissionantenna comprise second signals based on the data.

It should be noted that the above-mentioned examples illustrate ratherthan limit the invention, and that those skilled in the art will be ableto design many alternative examples without departing from the scope ofthe appended statements. The word “comprising” does not exclude thepresence of elements or steps other than those listed in a claim, “a” or“an” does not exclude a plurality, and a single processor or other unitmay fulfil the functions of several units recited in the statementsbelow. Where the terms, “first”, “second” etc. are used they are to beunderstood merely as labels for the convenient identification of aparticular feature. In particular, they are not to be interpreted asdescribing the first or the second feature of a plurality of suchfeatures (i.e. the first or second of such features to occur in time orspace) unless explicitly stated otherwise. Steps in the methodsdisclosed herein may be carried out in any order unless expresslyotherwise stated. Any reference signs in the statements shall not beconstrued so as to limit their scope.

1-37. (canceled)
 38. A method of transmitting signals, the methodcomprising: transmitting signals using one or more first subcarriersonly from a first antenna, wherein the signals transmitted from thefirst antenna comprise first signals based on data; and transmittingsignals using one or more second subcarriers different from the one ormore first subcarriers only from a second antenna, wherein the signalstransmitted from the second antenna comprise second signals based on thedata; wherein the data comprises one or more data portions; wherein thetransmitting the signals from the first and second antennas comprises,for each data portion, transmitting at least one first symbol using arespective one of the one or more first subcarriers from the firstantenna, and transmitting at least one second symbol using a respectiveone of the one or more second subcarriers from the second antenna; andwherein the first symbol and the second symbol are identical.
 39. Themethod of claim 38, wherein the method comprises refraining fromtransmitting signals using the one or more second subcarriers from thefirst antenna.
 40. The method of claim 38, wherein the method comprisesrefraining from transmitting signals using the one or more firstsubcarriers from the second antenna.
 41. The method of claim 38,wherein, for each data portion, the respective one of the one or morefirst subcarriers and the respective one of the one or more secondsubcarriers are non-adjacent.
 42. The method of claim 38: furthercomprising transmitting signals from one or more further antennas;wherein, for each further antenna, transmitting signals from the furtherantenna comprises transmitting signals using respective one or morefurther subcarriers only from the further antenna; wherein the signalstransmitted from the further antenna comprise second signals based onthe data; and wherein the respective one or more further subcarriers aredifferent from the one or more first subcarriers and the one or moresecond subcarriers.
 43. The method of claim 38, wherein the methodcomprises: encoding the data; mapping portions of the encoded data tofirst symbols according to a first modulation scheme; performing aninverse discrete Fourier transform on the first symbols to form thefirst signals; mapping portions of the encoded data to second symbolsaccording to a second modulation scheme; and performing an inversediscrete Fourier transform on the second symbols to form the secondsignals.
 44. The method of claim 43, further comprising interleaving thedata or the symbols.
 45. The method of claim 38, wherein the methodcomprises: forming the first signals by encoding portions of the dataaccording to a first encoding scheme to form first encoded data, mappingthe first encoded data to first symbols according to a first modulationscheme, and performing an inverse discrete Fourier transform andmultiplication by a complex waveform on the first symbols to form thefirst signals; and forming the second signals by encoding portions ofthe data according to a second encoding scheme to form second encodeddata, mapping the second encoded data to second symbols according to asecond modulation scheme, and performing an inverse discrete Fouriertransform and multiplication by a complex waveform on the second symbolsto form the second signals.
 46. The method of claim 38, wherein the datacomprises a training field and a data field.
 47. The method of claim 38,wherein the one or more first subcarriers comprise a first subset of aplurality of orthogonal subcarriers; and wherein the one or more secondsubcarriers comprise a second subset of the plurality of orthogonalsubcarriers.
 48. A method of receiving signals, the method comprising:receiving, at a first reception antenna, signals transmitted using oneor more first subcarriers only from a first transmission antenna,wherein the signals transmitted from the first transmission antennacomprise first signals based on data; and receiving, at the firstreception antenna, signals transmitted using one or more secondsubcarriers different from the one or more first subcarriers only from asecond transmission antenna, wherein the signals transmitted from thesecond transmission antenna comprise second signals based on the data;wherein the data comprises one or more data portions; wherein receivingthe signals transmitted from the first and second transmission antennascomprises, for each data portion, receiving at least one first symbolusing a respective one of the one or more first subcarriers transmittedfrom the first transmission antenna, and receiving at least one secondsymbol transmitted using a respective one of the one or more secondsubcarriers from the second transmission antenna; and wherein the firstsymbol and the second symbol are identical.
 49. The method of claim 48,wherein the method comprises receiving no signals transmitted from thefirst transmission antenna on the one or more second subcarriers. 50.The method of claim 48, wherein the method comprises receiving nosignals transmitted from the second transmission antenna on the one ormore first subcarriers.
 51. The method of claim 48, wherein, for eachdata portion, the respective one of the one or more first subcarriersand the respective one of the one or more second subcarriers arenon-adjacent.
 52. The method of claim 48: wherein the method comprisesreceiving signals transmitted from one or more further transmissionantennas; wherein, for each further transmission antenna, receivingsignals transmitted from the further transmission antenna comprisesreceiving signals transmitted using respective one or more furthersubcarriers only from the further transmission antenna; wherein thesignals transmitted from the further transmission antenna comprisesecond signals based on the data; and wherein the respective one or morefurther subcarriers are different from the one or more first subcarriersand the one or more second subcarriers.
 53. The method of claim 48,wherein the data comprises a training field and a data field.
 54. Themethod of claim 48, wherein the one or more first subcarriers comprise afirst subset of a plurality of orthogonal subcarriers; and wherein theone or more second subcarriers comprise a second subset of the pluralityof orthogonal subcarriers.
 55. The method of claim 48, furthercomprising: processing the first signals received at the first receptionantenna as a first single input, single output (SISO) system; andprocessing the second signals received at the first reception antenna asa second SISO system.
 56. The method of claim 48, further comprisingreceiving the first and second signals also at a second antenna.
 57. Themethod of claims 56, further comprising: processing the first signalsreceived at the first reception antenna and the first signals receivedat the second reception antenna as a first single input, multiple output(SIMO) system; and processing the second signals received at the firstreception antenna and the second signals received at the secondreception antenna as a second SIMO system.
 58. A non-transitory computerreadable recording medium storing a computer program product forcontrolling a transmitter, the computer program product comprisingprogram instructions which, when run on processing circuitry of thetransmitter, causes the transmitter to: transmit signals using one ormore first subcarriers only from a first antenna, wherein the signalstransmitted from the first antenna comprise first signals based on data;and transmit signals using one or more second subcarriers different fromthe one or more first subcarriers only from a second antenna, whereinthe signals transmitted from the second antenna comprise second signalsbased on the data; wherein the data comprises one or more data portions;and wherein transmitting the signals from the first and second antennascomprises, for each data portion, transmitting at least one first symbolusing a respective one of the one or more first subcarriers from thefirst antenna, and transmitting at least one second symbol using arespective one of the one or more second subcarriers from the secondantenna; and wherein the first symbol and the second symbol areidentical.
 59. A non-transitory computer readable recording mediumstoring a computer program product for controlling a receiver, thecomputer program product comprising program instructions which, when runon processing circuitry of the receiver, causes the receiver to:receive, at a first reception antenna, signals transmitted using one ormore first subcarriers only from a first transmission antenna, whereinthe signals transmitted from the first transmission antenna comprisefirst signals based on data; and receive, at the first receptionantenna, signals transmitted using one or more second subcarriersdifferent from the one or more first subcarriers only from a secondtransmission antenna, wherein the signals transmitted from the secondtransmission antenna comprise second signals based on the data; whereinthe data comprises one or more data portions; wherein receiving thesignals transmitted from the first and second transmission antennascomprises, for each data portion, receiving at least one first symbolusing a respective one of the one or more first subcarriers transmittedfrom the first transmission antenna, and receiving at least one secondsymbol transmitted using a respective one of the one or more secondsubcarriers from the second transmission antenna; and wherein the firstsymbol and the second symbol are identical.
 60. An apparatus fortransmitting signals, the apparatus comprising: processing circuitry;memory containing instructions executable by the processing circuitrywhereby the apparatus is operative to: transmit signals using one ormore first subcarriers only from a first antenna, wherein the signalstransmitted from the first antenna comprise first signals based on data;transmit signals using one or more second subcarriers different from theone or more first subcarriers only from a second antenna, wherein thesignals transmitted from the second antenna comprise second signalsbased on the data; wherein the data comprises one or more data portions;wherein the transmitting the signals from the first and second antennascomprises, for each data portion, transmitting at least one first symbolusing a respective one of the one or more first subcarriers from thefirst antenna, and transmitting at least one second symbol using arespective one of the one or more second subcarriers from the secondantenna; and wherein the first symbol and the second symbol areidentical.
 61. An apparatus for receiving signals, the apparatuscomprising: processing circuitry; memory containing instructionsexecutable by the processing circuitry whereby the apparatus isoperative to: receive, at a first reception antenna, signals transmittedusing one or more first subcarriers only from a first transmissionantenna, wherein the signals transmitted from the first transmissionantenna comprise first signals based on data; receive, at the firstreception antenna, signals transmitted using one or more secondsubcarriers different from the one or more first subcarriers only from asecond transmission antenna, wherein the signals transmitted from thesecond transmission antenna comprise second signals based on the data;wherein the data comprises one or more data portions; wherein receivingthe signals transmitted from the first and second transmission antennascomprises, for each data portion, receiving at least one first symbolusing a respective one of the one or more first subcarriers transmittedfrom the first transmission antenna, and receiving at least one secondsymbol transmitted using a respective one of the one or more secondsubcarriers from the second transmission antenna; and wherein the firstsymbol and the second symbol are identical.